Adds validation to check that package names do not collide within a job

TODO: delay the temporarily disabled validations about releases in jobs

Signed-off-by: Jesse Zhang <jz@pivotallabs.com>
User can specify release for each template in manifest

[finishes #63916864, #60722772]

Signed-off-by: Jesse Zhang <jz@pivotallabs.com>
Annotate the template with the job it belongs to

This gives clearer error message when the release is omitted but
ambiguous.